Bake in the preheated oven until tops spring back when lightly pressed, about 25 minutes. Transfer to a wire rack and let cool, at least 15 minutes.

Place chocolate and margarine in top of a double boiler over simmering water. Stir frequently, scraping down the sides with a rubber spatula to avoid scorching, until chocolate is melted, about 5 minutes. Stir 1 teaspoon cinnamon and 1/2 teaspoon cayenne pepper into the frosting.